The invention relates to a method of manufacturing, on a substrate, at least one electrode whose cross-section parallel to a main surface of the substrate is larger at the base than at the top in which method material for forming the electrode is deposited on the substrate via an apertured mask parallel to a main surface of the substrate, the material also growing on the mask in a lateral direction within the aperture during deposition.
Such an electrode may be conical or pyramid-shaped, but also, for example wedge-shaped. At this main surface the substrate may already be provided with, for example, metal tracks on which the material is deposited.
The invention also relates to an electrode manufactured by such a method, which electrode may function, for example, as an electron source (field emitter) or ionizer.
Such electron sources are particularly useful in flat display devices. The ionizers are notably used in scientific apparatus.
A method of the type mentioned in the opening paragraph is described in U.S. Pat. No. 5,007,873. In this method, the electrodes (field emitters) are obtained by depositing the electrode material through a mask on to the substrate by vapour deposition in which the material for manufacturing the electrodes is released from a source by electron beam vapour deposition. The greater part of the electrode material is deposited on the surface of the substrate perpendicularly or at a small angle with respect to the normal. Due to growth of electrode material in the lateral direction at the location of the apertures in the mask, a part of this material causes these apertures to become gradually smaller, and the cross-sections of the growing electrodes become smaller so that the electrodes acquire a pointed, for example, a conical shape.
If the electrode is used as a (field) emitter, it is necessary for a satisfactory emission that said point or cone has an acute apex angle. Moreover, to obtain a uniform setting throughout the image when using larger flat display devices having a plurality of emitters per pixel, there should not be too much spread in the shapes of the emitters. This means that the source from which the material is released should be placed far remote from the substrate. The vacuum installation to be used then becomes disproportionately large and expensive, while evacuation also takes a long time. Moreover, the material choice is limited when these types of methods (vapour deposition, electron beam deposition) are used, because measures should generally be taken to achieve relaxation of mechanical stress in the layer growing on the mask.